ISDN is the abbreviation for Integrated Services Digital Network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). ISDN used to be the preferred backup communications strategy for credit unions but has been replaced by VPN backup. New ISDN backup connections are no longer supported by CU*Answers.